Im3

Im3 is the Colicin Immunity Protein produced by E. coli cells alongside Colicin E3 to prevent the Colicin's RNase activity from killing the cell. Once the complex has been released by the producing E. coli it then binds to a target cell, and upon binding the immunity protein is released from the ColE3 cytotoxic domain.

3D structures of colicin-E3 immunitiy protein
Colicin Immunity Protein